1. Field of the Invention
The present invention relates to an inkjet printing apparatus that sequentially feeds printing media from a printing media storage unit to a printing head. The present invention particularly relates to an inkjet printing apparatus that enables performance of an ejection recovery process during a period extending from the end of printing for a previously fed printing medium to the start of printing for a succeeding printing medium.
2. Description of the Related Art
In an inkjet printing apparatus, ink supplied by an ink supply source, such as an ink tank, is ejected from the ejection ports of an inkjet printing head, as droplets, to form an image on a printing medium. Therefore, in the inkjet printing head (hereinafter referred to simply as the printing head), a plurality of liquid paths are defined that communicate with individual ports, and a common liquid chamber is formed that communicates with these liquid paths. Since the common liquid chamber is also connected to the ink supply port of the ink tank, ink from the ink tank is supplied to the individual liquid paths via the common liquid chamber. Further, ejection energy generation devices, which generate energy for the ejection of ink, are provided along the respective liquid paths, and when these ejection energy generation devices are driven, based on print data, ink droplets are ejected from the ejection ports. It should be noted that electrothermal conversion devices such as heaters, or electromechanical conversion devices, such as piezoelectric devices, are employed as the ejection energy generation devices. Further, in the specification and claims of the present invention, the portions constituted by the ejection ports and the liquid paths are called nozzles.
With this inkjet printing apparatus, when ink has not been ejected for an extended period of time while the liquid paths, over the same period, are filled with ink, the ink in the liquid paths may become viscous or sticky, causing the amount of ink ejected and the landing accuracy with which the ink is deposited to fluctuate, and an ejection malfunction to occur. Furthermore, if the ink becomes extremely viscous or sticky, clogging may occur and the ejection of ink through the ejection ports may be blocked.
In order to remove these inconveniences occasioned by the use of ink, a unique arrangement, which is not found in other printing apparatuses that do not employ ink, is provided for the inkjet printing apparatus. That is, an ejection recovery system is provided for the inkjet printing apparatus. This ejection recovery system cleans the liquid paths in the printing head and through the face (hereinafter referred to as an ejection port formation face) wherein the ejection ports are formed, and maintains an appropriate ejection function state for the printing head.
As one method employed by the ejection recovery system to effect the recovery of the ejection function, there is a so-called ejection recovery method that provides for the forcible ejection of viscous or sticky ink, through the ejection ports, by the application of a predetermined pressure to the liquid paths, and the subsequent introduction of new ink into the liquid paths. As the ejection recovery method, there are a pressure recovery method for applying pressure to the ink supply system, and a suction recovery method for sucking ink through the ink ejection ports, that together can forcibly ejection and remove viscous or sticky ink. Also available is a wiping recovery method whereby a wiping member is arranged so that it contacts the ejection port formation face, and whereby viscous or sticky ink attached near the ejection ports is removed by moving the wiping member across the ejection port formation face.
However, for all the above described recovery methods available for an inkjet printing apparatus, a comparatively long time is required. Therefore, when one of these recovery methods is employed during a printing or a printing related operation, the period required to complete the printing is increased, and overall, the printing speed is reduced. Therefore, as one method for maintaining the ink in the liquid paths in an appropriate ejection state without the printing speed being greatly deteriorated, a recovery method called a preliminary ejection is also employed. According to this preliminary ejection method, ink that is not directly related to printing is ejected to a predetermined ink receiving member. When this preliminary recovery is performed for ejection ports for which the ejection frequency is low, ink in the liquid paths can be maintained in an appropriate ejection state.
In Japanese Patent Application Laid-open No. 2000-094659, an inkjet printing apparatus is described that includes a mechanism for recovering the ejection function of a printing head during the operation for feeding a printing medium. According to the inkjet printing apparatus described in this publication, the preliminary operation of a printing head is started when the feeding operation is begun or while the feeding operation is being performed, so that for a printing medium, the period from the start of the feeding operation until the start of printing can be reduced. Further, in U.S. Pat. No. 6,702,274 is disclosed a proposal related to an increase in the sheet feeding speed for sequential printing. An inkjet printing apparatus described in this patent can independently drive a feeding mechanism, a sheet conveying mechanism and a carriage mechanism. In the inkjet printing apparatus, information obtained by a paper sensor as well as the length of a printing medium are entered, and one or both of these entries are employed to control the timing of the feeding operation. For example, the timing at which to start the feeding of a succeeding printing medium is determined simply in accordance with the length of the printing medium, irrespective of any information obtained by the paper sensor. Or, after the leading edge of the succeeding printing medium has reached a position to the front of the paper sensor, a decision is made as to whether the trailing edge of the current printing medium has passed the paper sensor, and dependant on the result obtained, a determination is made as to whether the feeding operation should be continued.
As described above, according to the inkjet printing apparatus described in U.S. Pat. No. 6,702,274, the timing for the feeding of a succeeding printing medium can be controlled in accordance with the performance progress for the preceding one, which is being processed, so that a minimum distance, relative to the succeeding printing medium, can be designated. In addition, when differently sized printing media are employed or there is a feeding mechanism error, such as minor slippage, the double feeding of printing media or the deterioration of the search function accuracy will not occur. Therefore, fast sequential feeding can be stably performed during sequential printing, and the printing speed can be increased.
In addition, recently, the sizes of ink droplets that are ejected from printing heads have steadily been reduced, and accordingly, images having higher resolutions and improved image quality are being obtained. As a result, and in direct relation to the reductions in the sizes of the ink droplets, the diameters of the ejection ports in printing heads that are currently being produced have become proportionally smaller, and the ejection recovery process has assumed an extremely important role in the maintenance of a stable ejection state for these printing heads. Thus, for inkjet printing apparatuses generally, the ejection recovery process is most effectively performed by employing a period before the printing of a printing medium has begun.
For example, when a printing operation is to be performed for a first printing medium, a predetermined time period is required for the feeding process, beginning at the start of the feeding operation and continuing until the start of the printing operation. Therefore, the ejection recovery process for the printing head can be performed during this period.
In a case where, sequential printing is performed with a sequential feeding operation, a general type of ink jet printing apparatus as previously mentioned begins to feed a succeeding printing only after the trailing edge of a preceding one has passed the paper sensor. Thus, during the sequential printing operation, a sufficient period is available for the performance of the ejection recovery process before the printing of the succeeding printing medium is started.
According to the inkjet printing apparatus disclosed in Japanese Patent Application Laid-open No. 2000-094659, the ejection recovery process can be performed during the feeding operation; however, an extended period of time is required, lasting from the end of the printing of the preceding printing medium to the start of the printing of the succeeding printing medium. Therefore, when sequential printing is to be performed, since the period for the completion of the entire printing operation is extended, the speed at which the printing is performed must be increased.
On the other hand, when high-speed sequential printing is performed by the inkjet printing apparatus described in U.S. Pat. No. 6,702,274, the period of time for the feeding can be reduced because the distance between the preceding printing medium and the succeeding printing medium is shortened. However, the time margin for the performance of the ejection recovery process is reduced. Therefore, depending on the time required for ejection recovery, the feeding of the succeeding printing medium must be delayed in order to provide an adequate period for the performance of the ejection recovery operation. That is, were the inkjet printing apparatus disclosed in U.S. Pat. No. 6,702,274 or in Japanese Patent Application Laid-open No. 2000-094659 to be employed, the overall printing speed would be reduced.